During the 20th century, brain neurosurgery has advanced via the introduction of microsurgical techniques, the development of new tools such as aneurysm clips, and the description of new operative approaches. Surgeons have developed elegant mechanisms to remove parts of the bones making up the skull (craniotomy) and operate on structures deep within the brain while attempting to minimize complications relating to the approach. The surgical approach to the intracranial and spinal subarachnoid space has historically included skin incision, dissection to either the cranium or spinal bony covering, removal of some bone, and dissection through the meninges to gain access to the neurological structures. While imaging modalities became integrated into diagnostic evaluations, only at the end of the last century were significant attempts made to integrate computed tomography, angiography, and most recently magnetic resonance (MR) scanning into the actual surgical procedures.
Unfortunately, craniotomy has limited the applicability of some present imaging modalities because the surgeon cannot simultaneously stand at the patient's head to operate on the brain via craniotomy, maintain sterility, and scan the brain using a large scanning apparatus that requires the patient to be held within it. There are limits to the ability to conveniently perform such surgery using currently-available imaging devices due to a conflict between the devices for acquiring images and the methods of operating on the brain.
An additional concern is that, while the brain surface is readily accessed via conventional craniotomy, the approach to deeper structures is progressively more difficult. The brain is often retracted after the craniotomy to facilitate access to different areas in and around the brain, and in some cases there is the need to remove brain tissue to gain access. Both retraction and removal create potential problems with maintaining sterility and avoiding direct injury to tissue, as well as the problem of putting tissue back into place without causing injury.
During the last 20 years, the development of endovascular neurosurgery has resulted in the creation of specialized devices for application within arteries. These devices include not only catheters and guidewires, but also embolic materials that can be introduced via catheters, thereby enabling the enhancement of some procedures that are performed via craniotomy following embolization. In some cases, the need for craniotomy has been eliminated. However, access is limited to that achieved from within blood vessels.